Sorption Behavior of 4-Chlorophenol from Aqueous Solutions By a Surfactant-modified Mexican Zeolitic Rock in Batch and Fixed Bed Systems

The removal of 4-chlorophenol from aqueous solutions by both a Mexican clinoptilolite-heulandite zeolitic rock and the modified zeolitic material with the surfactant hexadecyltrimethylammonium bromide (HDTMABr), using batch and packed-bed (column) configurations, was investigated. The unmodified zeolitic rock did not show any adsorption of 4-chlorophenol. The effects of pH, contact time and concentration of 4-chlorophenol on the adsorption process by the surfactant modified material were examined. The sorption of 4-chlorophenol was not affected by the pH range from 4 to 9.5. 4-chlorophenol retention reached equilibrium in about 18 h and the rate of 4-chorophenol adsorption by the modified material was faster in the first 10 h than later. The experimental data were treated with the models: pseudo-first order, pseudo-second order, fractional power and Elovich models. Although, the last three gave correlation coefficients higher than 0.96, the pseudo-second order model was the best to describe the reaction rate. The experimental data follow a linear isotherm which is characteristic for sorption of organic solutes by the partition mechanism. The Bed Depth-Service Time Model was applied to the sorption results in order to model the column operation. The results showed that the surfactant modified zeolitic rock could be considered as a potential adsorbent for 4-chlorophenol removal from aqueous solutions.     

Kinetic Study of BTEX Removal Using Granulated Surfactant-Modified Natural Zeolites Nanoparticles

Increasing release of organic pollutants to the environment has caused one of the largest world crises for water resources. Volatile organic compounds are toxic monoaromatic pollutants of soil and water. In this research, natural zeolite nanoparticles were produced mechanically by means of a milling technique, modified using two cationic surfactants of hexadecyltrimethylammonium chloride and n-cetyl pyridinium bromide and formed as granules using a novel technique already developed by our group. The granulated adsorbents were used to uptake benzene, toluene, ethylbenzene, and xylenes (BTEX) from contaminated water. Two intra-particle diffusion models (i.e., Weber and Morris and Vermeulen models) and three surface reaction models (i.e., pseudo-first order, pseudo-second order, and Elovich) were applied to evaluate the kinetics of adsorption and the best fitted model was chosen. Results of the adsorption kinetic evaluations were shown that uptake of granulated nanozeolites are higher than natural zeolites (in the order of four). Kinetic results revealed that the adsorption follows a pseudo-second order indicating existence of chemisorption in the studied conditions. It was noticed that the intra-particle diffusion is prevailing in the first stage of adsorption for a relatively short time (i.e., first 25 min).     

Removal of Mercury Ions from Mixed Aqueous Metal Solutions by Natural and Modified Zeolitic Minerals

Research works on the removal of mercury from water by zeolitic mineralshow that small quantities of this element are sorbed. In this work the mercury sorption from aqueous solutions in the presence and absence of Cu(II), Ni(II) and Zn(II) onto a Mexican zeolitic mineral unmodified and modified with cysteamine hydrochloride or cystamine dihydrochloride was investigated in acidic pH. The zeolitic minerals were characterized by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction and FTIR. The sorption kinetics behavior and the retention isotherms for mercury were determined in the natural and treated zeolitic mineral samples. It was found that the amounts of sulfur on the modified zeolitic minerals were 0.375 (cysteamine hydrochloride) and 0.475 (cystamine dihydrochloride) mmol g^-1, which were not saturated to their total capacities of adsorption for the maximum concentration used (0.310 mM). Under the experimental conditions, the retention of mercury was the highest for the zeolitic minerals treated with the organic compounds, with adsorption capacities ranging from 0.0107 to 0.0509 mmol Hg g^-1.The retention was not affected by the presence of others heavy metals studied in this work as expected.     

生物炭与沸石混施对不同污染土壤镉形态转化的影响

采用室内培养模拟了低(1.0 mg/kg)、高(10 mg/kg)镉污染的土壤,通过向镉污染土壤中添加0.4%,2%,10%的1∶1的生物炭和沸石的混合物,探究了生物炭及沸石混施对不同程度镉污染土壤的pH和镉形态变化的影响。结果表明:2种不同程度镉污染土壤的pH均较CK有所提高,且随钝化剂用量的增加而增大。随着培养时间的延长,低污染土壤pH呈现降低趋势,而高污染土壤pH先升高后降低最后趋于稳定。培养后期,低污染和高污染土壤在混合物添加量分别为2%和10%时有效态镉降低比例最大,降低比例分别为56.78%和27.33%。各处理土壤随生物炭和沸石混合物添加量的增加交换态镉降低比例逐渐增大,培养后期,低污染土壤的交换态镉较CK分别降低8.35%,13.81%,20.65%,高污染土壤的交换态镉较CK分别降低10.02%,22.34%,33.01%。各处理的钝化剂能够明显的降低交换态镉的含量,增加碳酸盐结合态、铁锰氧化物结合态、有机结合态和残渣态镉的含量,低污染土壤的有机结合态明显高于高污染土壤。由此可见,生物炭与沸石混施能够降低土壤重金属的生物有效性,为农田土壤修复奠定了理论基础。     

Nitrate Sorption in a Mexican Allophanic Andisol using Intact and Packed Columns

Abstract

Contamination of groundwater by nitrate is a worldwide environmental issue. A better knowledge of nitrate sorption characteristics by soils contributes to efficient fertilizer use and prevents aquifer contamination. In volcanic soils, nitrate sorption is induced by variable charges due to the presence of amorphous materials and aluminum (Al) and iron (Fe) oxides. Anion transport in packed and intact columns was investigated in a Mexican Allophanic Andisol, under different permanent flow regimes in unsaturated conditions and several NO₃ ^?‐N and Br^? input concentrations. In the packed columns, the NO₃ ^?‐N adsorption in the soil was nonlinear. In the intact columns, the retardation coefficient variation was directly correlated to the increase of amorphous material with depth. The presence of preferential flow in the intact columns significantly increased the mobility and velocity of nitrate moving through the columns, whereas in the packed columns, NO₃ ^?‐N fate was only affected by soil chemical composition and mineralogy.     

Natural Nitrogen-15 Abundance of Ammonium Nitrogen and Fixed Ammonium in Soils

The present article deals with the natural nitrogen-15 abundance of ammonium nitrogen and fixed ammonium in different soils.Variations in the natural ^15N abundance of ammonium nitrogen mineralized in soils under anaerobic incubation condition were related to soil pH.The δ ^15N of mineralizable N in acid soils was lower but that in neutral and calcareous soils was higher compared with the δ ^15N of total N in the soils.A variation tendence was also found in the δ ^15N of amino-acid N in the hydrolysates of soils.The natural ^15N abundance of fixed ammonium was higher than that of total N in most surface soils and other soil horizons,indicating that the increase of δ ^15N in the soil borizons beneath subsurface horizon of some forest soils and acid paddy soils was related to the higher δ ^15N value of fixed ammonium in the soil.     

混凝法去除镉及含镉絮体的稳定性研究

以广西龙江河的河水和底泥为研究对象,通过混凝沉淀实验验证聚合氯化铝(PAC)对人工配制的超标40倍河水中镉的去除效果,并考察不同pH模拟洪水对含镉絮体释镉的影响。结果表明:在pH为(9.00±0.05)的浑浊河水中,PAC对河水中的镉具有很好的去除效果,投加PAC后12h,PAC对河水中镉的去除率可达到98.52%～99.42%;在pH为(6.00±0.05)～(8.00±0.05)的模拟洪水过后72h内,河水中的Cd2+浓度均低于5μg/L,含镉絮体不释镉或少量释镉,稳定性较好;在pH为(5.00±0.05)的模拟洪水过后72h内,河水中的Cd2+浓度部分高于5μg/L,含镉絮体释镉量较大,稳定性较差。因此,在龙江河的生态环境影响后评估工作中应加强洪水期的监测。     

Adsorption of Cadmium on Bed Sediments of River Hindon: Adsorption Models and Kinetics

The adsorption characteristics of cadmium on bed sediments ofriver Hindon in western Uttar Pradesh (India) have been studied.The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time, particlesize and temperature has been studied. The optimum equilibrationtime was found to be 60 min, which was independent of initialconcentration of cadmium ions. The adsorption curves were smoothand continuous leading to saturation, suggesting the possible monolayer coverage of cadmium ions on the surface of the adsorbent. The adsorption of cadmium increased with an increasein pH. Furthermore the adsorption of cadmium increased with increasing adsorbent concentration and decreased with adsorbentparticle size. The important geochemical phases, iron and manganese oxide, support the adsorption of cadmium ions. The adsorption data were analysed using the Langmuir and Freundlichadsorption models to determine the mechanistic parameters relatedto the adsorption process. Thermodynamic parameters, viz., freeenergy change, enthalpy change and entropy change, were alsodetermined. The negative values of free energy change (ΔG°) indicated the spontaneous nature ofthe adsorption and positive values of enthalpy change (ΔG°) suggested the endothermic nature ofthe adsorption process. The intraparticle diffusion of cadmium through pores in the adsorbent was found be the main rate-limiting step.     

天然和热活化蛇纹石对土壤镉赋存形态的影响

以天然蛇纹石粉为原料,应用马弗炉制备不同温度(550℃和700℃)的热活化蛇纹石,通过室内培养试验,探究不同剂量(分别为土重的1%,3%,5%)的天然和热活化处理的蛇纹石对外源镉污染土壤中镉赋存形态的影响。结果表明,土壤pH值随蛇纹石用量增加而增加,随培养时间延长呈现先降低后趋于稳定的趋势,但均显著高于对照。高剂量700℃热活化蛇纹石对土壤pH值影响最大,培养60d时与对照相比提升了1.98个单位。添加天然蛇纹石、550℃和700℃热活化蛇纹石均能降低土壤可交换态镉的含量,与对照相比分别降低了17.42%~28.32%,28.99%~39.63%,33.11%~53.72%。相关性分析表明,各培养时期土壤可交换态镉的含量与土壤pH值呈现极显著负相关关系。各处理对土壤镉各形态含量的影响差异不同,显著降低了土壤可交换态镉的含量,不同程度地提高了碳酸盐结合态、铁锰氧化物结合态和残渣态镉的含量,对有机物结合态镉的影响并不明显。总的来说,蛇纹石添加入土壤后能够提高土壤pH值,促使可交换态镉向其他生物可利用性较低的镉形态转变,且不同剂量、不同热活化温度间存在显著差异。     

Effect of Fixed Media Surface Area on Biofouling and Nutrients Removal in Fixed Film Membrane Bioreactor Treating Sewage at Medium and High Fluxes

This study investigates effects of fixed film surface area increment on removal efficacy and biofouling in membrane bioreactor (MBR). For this purpose, a lab-scale membrane bioreactor was used. Domestic wastewater was fed into it. Three different trials were conducted at different fluxes; 15, 20, and 25 L/m²/h (LMH). Every trial was conducted using four different scenarios by varying surface area of fixed media viz. 0, 100, 150, and 200 m²/m³. Removal of pollutants viz. chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic content (TOC), total Khjdel nitrogen (TKN), and phosphorous was studied. In addition, cake resistance, pore resistance, and total resistance were also observed for aforementioned scenarios. The results demonstrated that pollutant removal efficiencies increased as the surface area per unit volume of bioreactor was increased. Conversely, the removal efficiency decreased with increase in the fluxes. In the case of biofouling, it increased while increasing the surface area or flux. The fixed media surface area increments proved beneficial in terms of removal efficiencies but at the cost of reduced operation time of MBR.     

Removal of Arsenic, Boron, and Selenium from Excavated Rocks by Consecutive Washing

This paper describes the leaching behavior and release mechanisms of arsenic (As), boron (B), and selenium (Se) from excavated rocks using sequential extraction for solid-phase fractionation, batch experiments with pH variation, and consecutive batch experiments with changes in the solid?Cliquid mixing ratios. Arsenic in the excavated rock was mostly found with the sulfides/organic matter fraction while majority of the leachable B and Se were associated with the exchangeable phases. The leaching of As was strongly pH dependent, Se was pH dependent only around the acidic region, and B was pH independent. Consecutive washing technique with deionized water effectively lowered the B and Se concentrations in the leachate below the drinking water standards of Japan, but was inefficient in the removal of As. Arsenic exhibited non-conservative leaching behavior and its movement was affected by processes like dissolution, precipitation, and pyrite oxidation. In contrast, B and Se behaved more conservatively, resulting in their easy removal from the excavated rock by simple washing and dilution.     

天然与改性沸石对土壤Cd污染赋存形态的影响研究

试验采用室内培养的方法,研究了不同剂量天然沸石、改性沸石(氯化铵和氯化钙改性)对土壤中重金属Cd赋存形态的影响。结果表明,同一剂量天然沸石与氯化钙改性沸石处理中随时间推移土壤p H先升高后降低,最后趋于稳定,氯化铵改性沸石处理则呈现持续下降的趋势。在整个培养时期,氯化铵改性沸石处理组中土壤交换态Cd含量呈先降低后升高的趋势,在30 d时达到最低值;氯化钙改性沸石与天然沸石处理土壤交换态Cd呈现持续降低的趋势,三者土壤交换态Cd分别降低了18.74～30.82 mg kg~(-1)、18.5～30.12 mg kg-1、13.71～28.28 mg kg~(-1)。三种处理对土壤中残渣态镉的转化率为氯化铵改性沸石氯化钙改性沸石天然沸石,50 d时三者残渣态镉含量分别增加了21.48%、18.23%、14.08%。根据土壤pH与土壤交换态Cd含量相关性分析表明,二者呈显著负相关,土壤p H值与改良剂修复土壤重金属污染的修复效率密切相关。     

Removal of Copper and Cadmium Ions from Diluted Aqueous Solutions by Low Cost and Waste Material Adsorbents

The sorption of copper and cadmium ions using activated carbon,kaolin, bentonite, diatomite and waste materials such as compost,cellulose pulp waste and anaerobic sludge as sorbents is reported. Equilibrium isotherms were obtained for the adsorption of these metals in single and binary solutions. Bentonite presented the highest adsorption capacities for both copper and cadmium. A competitive uptake was observed when both metals are present; copper being preferentially adsorbed by all materials with theexception of anaerobic sludge. Equilibrium data were fitted toLangmuir and Freundlich models, with satisfactory results for most of the adsorbent-metal systems studied.Of all the adsorbents studied, bentonite and compost presentedthe highest removal efficiencies, reaching 99% for copper whencadmium is also present, for initial solution concentrations ofup to 100 mg L^-1. Anaerobic sludge has a greater preferencefor cadmium, even in the presence of copper, with removal efficiencies of 98% for similar concentrations to those mentioned above.     

Natural Removal of Crude and Heavy Fuel Oil on Rocky Shorelines in Arctic Climate Regimes

Water, Air, &; Soil Pollution - The ecotoxicity of nickel depends on water quality characteristics such as pH and dissolved organic carbon. Bioavailability models to predict nickel toxicity have...     

Effects of Various Parameters on Removal of NO2 Gases in Fixed Beds by Adsorption on Sepiolite

Removal of NO₂ gases in fixed beds was investigatedby using brownish, whitish and regenerated whitish sepioliteand perlite as adsorbents. For this purpose, NO₂ wasproduced by reaction of copper with nitric acid. The producedgas was mixed with air and the mixture was sent through a fixedbed. Studies were conducted using various gas flow rates,NO₂ concentrations, packing sizes and heights of bed.Remaining NO₂ within the gas mixture leaving the column,unadsorbed on packing, was further absorbed by passing itthrough a series of washing bottles, filled by a solution ofNaOH. At the end of the study, it was observed that theadsorption capacity of sepiolites, especially whitishsepiolite, was much higher than that of perlite. Additionally,it was seen that its adsorption capacity increased withincreasing bed height, particle size, NO₂ concentrationand decreasing gas flow rate.     

微曝气生态浮床水芹吸收NP的特性及其对系统去除NP贡献的研究

针对污染河水黑臭缺氧、NH4^＋—N含量高等问题,研发了一种“漂浮载体悬挂弹性生物膜填料＋水生植物并辅以人工微曝气系统”的微曝气生态浮床系统,以漂浮植物水芹为例研究了系统中水芹对N、P的吸收特性和去除作用。结果表明,随着水芹的生长其生物量干重显著增加,生长80d左右时总生物干重在2497．2—3144．4g·m^-2之之间,上、下部生物量比平均为13．4。不同部位水芹N、P的含量不同,总的趋势为含N量叶〉根〉茎,含P量茎〉根〉叶。不同生长时间水芹N、P含量及其吸收速率不同：随着水芹的生长,组织内N、P含量逐渐降低,N的吸收速率总趋势为60-80d〉35-60d〉1-35d,P的吸收速率总趋势为35-60d〉1-35d〉60-80d。而随着水芹的生长吸收N、P的总量却在逐渐增加,吸收N的总量从17．69g·m^-2增加到61．66g·m^-2,吸收P的总量从4．99g·m^-2增加到13．55g·m^-2,这主要取决于自身的生物量和N、P的含量。水芹对N、P的积累主要集中在上部,分别占N、P吸收总量的92．2％-93．4％、92．5％～93．1％。水芹生长35、60、80d时,吸收N量占系统TN去除量的比率分别为4．50％、6．06％和6．87％,水芹对P的吸收量分别占系统去除P总量的18．53％、26．82％、22．00％。水芹对N、P的吸收仅是微曝气生态浮床净化系统去除N、P的一个途径,但水芹根际微生物的作用不可忽视。     

Copper Biosorption by Biomass of Marine Alga: Study of Equilibrium and Kinetics in Batch System and Adsorption/Desorption Cycles in Fixed Bed Column

Copper biosorption onto chemically modified biomass of marine alga Sargassum filipendula was investigated in a batch reactor and a fixed bed column. Experiments were carried out in the batch reactor to obtain kinetic and equilibrium data and to assess the copper desorption efficiency of different eluent solutions. The pseudo-first-order, pseudo-second-order, and Langmuir kinetic models were used to correlate kinetic data. The experimental data fitted well to the pseudo first order and Langmuir kinetic models. Langmuir and Freundlich models were applied to describe the equilibrium data obtained at a fixed temperature of 30°C and at pH values of 3.0, 4.0, 5.0, and 6.0. The maximum capacities of copper biosorption onto the algal biomass were 1.43, 1.59, 2.40, and 2.36 mequiv./g at pH 3.0, 4.0, 5.0, and 6.0, respectively. The efficiencies of two eluent solutions (calcium chloride and hydrochloric acid) for copper removal from the biomass were evaluated at different concentrations (0.1, 0.2, 0.5, and 1.0 mol/L). The efficiencies of the calcium chloride solutions varied from 1% to 14%, while efficiencies varying from 95% to 99% were obtained when hydrochloric acid solutions were applied. Three adsorption/desorption cycles were carried out in a fixed bed column using 0.1 mol/L hydrochloric acid as eluent solution. The results showed that an increase in the number of cycles led to a reduction in the adsorption capacity of the alga. The desorbed copper fraction presented no significant variation, remaining around 63% in the three adsorption/desorption cycles.     

Comparative Kinetic Study of Carrier Type in a Moving Bed System Applied to Organic Matter Removal in Urban Wastewater Treatment

In recent years, moving bed systems have been shown as an efficient technology in wastewater treatment and particularly in the treatment of urban effluents. This paper presents the results obtained for three different carriers in organic matter removal, analysing the influence of hydraulic retention time (HRT) and the filling ratio, as well as the kinetic constants of each carrier used. During the research, differences in the organic matter removal were observed under different conditions studied as a result of physical and geometrical characteristics of each carrier and their hydraulic behaviour. Two of the three carriers studied in this research had similar yields compared to the third carrier that presented lower rates of organic matter removal and lower kinetic constants than the other two. Carriers 1 and 2 obtained removal rates of organic matter in the form of soluble chemical oxygen demand (sCOD) above 50% for intermediate and higher filling ratios with HRTs of 15, 10 and 15 h, respectively. The maximum values obtained for carrier 1, 2 and 3 were 56.97%, 58.92% and 46.13%, respectively, under 15 h of HRT and 50% of filling ratio. The kinetic constants obtained by respirometry showed a similar trend to the values obtained from sCOD removal.     

适合地上匍匐茎水生植物的浮床设计及其对富营养化水体脱氮除磷的实效研究

采用分株繁殖获取空心莲子草、大聚藻、蕹菜幼苗,以根据地上匍匐茎植物独有的特点设计的新型网式浮床为载体,以400L大型水箱为容器,将这3种地上匍匐茎水生植物应用其中,探究地上匍匐茎水生植物在漂浮条件下对富营养化水体氮磷的真实净化能力,并与传统浮床的同类研究进行对比。结果表明,3种地上匍匐茎水生植物在网式浮床中生长状况良好,空心莲子草对氮的净化能力为0.643 0~1.563 3mg/(g·d),对磷的净化能力为0.012 7~0.142 0mg/(g·d);大聚藻对氮的净化能力为1.475 0~4.318 5mg/(g·d),对磷的净化能力为0.070 3~0.250 0mg/(g·d);蕹菜对氮的净化能力为3.114 5~4.505 0mg/(g·d),对磷的净化能力为0.179 0~0.372 5mg/(g·d);3种植物在网式浮床中对富营养化水体的净化能力均明显高于传统浮床同类研究结果。网式浮床能发掘地上匍匐茎水生植物对富营养化水体的净化潜力,比传统浮床更适用于地上匍匐茎水生植物。